What is the use and specific meaning of "-al" adjectives as nouns?

Question

I was thinking about the tone and syntactic tendencies in scholarly work and I thought of something that may occur in it, but doesn't seem to occur in more casual prose. You may have the word "the" followed by some adjective ending in the suffix "-al". An example of this right off the bat is the title of a book: The Primacy of the Political. You might also get something talking about "the psychosexual" or "the metaphysical"; as I've said, it seems mostly to show up in studious material.

This question asks about the use of adjectives as nouns in a more general sense, with the answer being a combination of metonymy and ellipsis. The trouble I have here is that those examples are very concrete and the ellipsis is easily understood through context, describing people or things. As far as I can tell, the adjectives begin used as nouns that I'm referring to seem to talk about something a lot more categorically broad and abstract. I'm not entirely certain though, and I was hoping someone might be able to weigh in on what exactly this specific type of use of adjectives as nouns means, and where/why it occurs.

Answer 1

It seems to me to be the same combination of metonymy and ellipsis described in the question you link. "The political" can be read as "that which is political" (seemingly, in the case of that book, in contrast to that which is "antipolitical.")

A consistent, but inelegant, phrase to add in afterward would be "things" (e.g., "the political things," "the metaphysical things," etc.). It could also be "the metaphysical/psychosexual aspects of the matter," in your other examples, though it doesn't work as well for "political."

All are omitting the same sort of "things"-type phrase, and all are describing a class of things by one of their attributes.